1. Field of the Invention
Aspects of the present invention relate to electrolytes for redox flow batteries and redox flow batteries including the electrolytes, and more particularly, to electrolytes for redox flow batteries having high energy density and long lifetime and redox flow batteries including the electrolytes.
2. Description of the Related Art
Secondary batteries are highly efficient energy storage systems that are widely used in small mobile phones and middle and large power storage devices. Specifically, secondary batteries are used as main core parts in semiconductor and liquid crystal devices, acoustic devices, and information and communication devices such as mobile phones and laptops. More recently, they have begun to be used as power sources in hybrid cars.
Such power storage systems require stable energy supply and high energy conversion efficiency. Recently, redox flow batteries have come into the spotlight as secondary batteries having a large capacity and high durability, which are most suitable for large-scale power storage systems.
Unlike other batteries, the active material of the redox flow batteries exists as ions in an aqueous state instead of a solid state, and the redox flow batteries have nechanisms of storing and generating electric energy according to the oxidation/reduction reaction of each ion in a cathode and an anode.
In other words, redox flow batteries include an electrolyte solution in which an active material of an electrode is dissolved in a solvent. The cathode is oxidized and the anode is reduced when a redox flow battery including a catholyte and an anolyte having different oxidation states is charged, and the electromotive force of the redox flow battery is determined by the difference between standard electrode potentials (E0) of a redox couple forming the catholyte and the anolyte. In addition, the catholyte and the anolyte are supplied from respective electrolyte solution tanks by a pump. The redox flow batteries simultaneously have a quick oxidation and reduction reaction rate on the surfaces of the cathodes and anodes, like typical batteries, and have large output characteristics, like fuel cells.
Recently, to enhance the low energy density of redox flow batteries, research into a method of operating a redox flow battery at a higher voltage range by using organic-based electrolytes instead of electrochemically unstable aqueous electrolytes has been actively conducted. In this regard, the concentration of metal salts in the organic-based electrolytes directly affects the energy density of the redox flow batteries and thus it is necessary to enhance the solubility of the metal salts in an organic solvent.